1. Field of the Invention
The present invention relates to a vacuum pump having a high-speed rotor, and an anti-friction bearing for rotatably supporting the rotor and including an inner ring, an outer ring, a rolling body, and a cage for the rolling body both the rolling body and the cage being located in an intermediate space defined by the outer and inner rings.
2. Description of the Prior Art
For many years, vacuum pumps with a high-speed rotor have successfully been used for producing vacuum with a low absolute gas pressure. Vacuum pumps of turbomolecular or Holweck types have been used with a particular success. For rotatably supporting the rotor, as a rule, magnetic or anti-friction bearings are used. Despite a great progress in reduction of manufacturing costs of magnetic bearings, the use of anti-friction bearings as operational bearings in vacuum pumps still cannot be eliminated.
Anti-friction bearings require lubrication in order to achieve as long as possible service life. The supply of lubricant in anti-friction bearings can be divided in two categories.
To the first category, grease-lubricated bearings belong. In the grease-lubricated bearings, lubricant is embedded in a matrix, with a small amount of the lubricant being fed therefrom. The problem with this category of bearings consists in that in the majority of cases, the grease can be replaced only with great costs and therefore a vacuum pump must be produced with a certain amount of grease already being put into the vacuum pump during production. This is associated with certain drawbacks such as, e.g., reduction in the rotor temperature that can be achieved. This is because the rotor heat is essentially removed by the anti-friction bearing, leading to the heating of the lubricant. Because the grease always remains in the bearing, there is a danger that it would be destroyed by high temperature.
To the second category belong anti-friction bearings through which lubricant flows. A lubricant flow can be produced by a lubricant pump when a large amount of the lubricant is required, or obtained by capillary forces at small amounts of lubricant. Such a bearing support is disclosed in German Publication de 10 2006 053 237.
Though the service life of vacuum pumps with the anti-friction bearings of the second category is greater than with those of the first category, wear was noticed that was greater than expected.
Accordingly, an object of the present invention is to increase the service life of a vacuum pump with a high-speed rotor supported by at least one anti-friction bearing.